With hand tools that are driven electrically, such as drilling machines that are commercially operated, it is important, for using the working hours as efficiently as possible, to be able to schedule maintenance measures in conjunction with the hand tools accurately enough, in particular in the context of measures relating to replacing the carbon brushes. Hence, it is ensured that the required wear parts are available in good time for the anticipated maintenance date and that lost working hours due to unexpected maintenance work can be avoided to the greatest extent.
In order to inform about the condition of the carbon brushes in good time and to provide a warning that the wear limit of the carbon brushes will soon be reached, it is therefore standard practice to provide carbon brushes with a so-called stranded indicating wire, which is formed or arranged in the brush body of the carbon brush such that, for announcing that the wear limit will soon be reached, an electrically conductive contact between the stranded indicating wire and the slip ring or the commutator of the drive engine of the hand tool is established.
In order to avoid damage to the hand tool as a result of the operation of the hand tool being continued even after the wear limit has been reached, the indicating function that is fulfilled by the stranded indicating wire can additionally be complemented with a disconnection function, which brings about a compulsory interruption in the operating current supply via the stranded wire that carries the (operating) current. Said disconnection function can be configured as a mechanical disconnection mechanism. Thus, a disconnection mechanism is known, for instance from the document EP 0 512 234 BI, which mechanism is formed in the brush body as a component assembly that is composed of several components. The disconnection mechanism features a disconnection nipple which is formed so as to be electrically insulating, and which, being spring-preloaded, is received in a receiving bore. For generating the spring-preload, a pressure spring being coupled to the disconnection nipple is supported at a compressed filling compound which has been filled into the receiving bore, and which consists of a metal powder as a rule. By mechanically lifting the carbon brush off the commutator or off the slip ring of the electric engine, the interruption in the current supply is guaranteed.